This invention is directed generally to a water heating system and is specifically directed to that type of system utilized in residential households, although the system can be adapted to commercial usage. The system is uniquely designed and adapted for utilization with relatively small capacity hot water systems which may have a storage tank capacity in the order of thirty to two hundred gallons.
Water heating systems presently utilized are generally of an electrically heated type or of a combustion type having a burner which is fueled by either natural gas or oil. The types of water heating systems utilizing electrical power generally include one or two electrical resistance heating elements and temperature control systems are provided to operate those heaters in accordance with the temperature of the water within the storage tank. Usually, if two such heaters are provided, they are placed at relatively vertically spaced positions and are interconnected with an electrical control system which enable operation of the units to most effectively provide heating of the water. These water storage tanks also have cold water inlets and hot water outlets with the cold water normally entering at the bottom of the tank. This is to obtain the advantages of a thermal convection distribution of water within the tank and thus the hottest water will be at the upper end of the tank where it is first withdrawn for use. Accordingly, a heating element located near the bottom, or within a bottom zone of the tank, will be effective in heating the cold water as it is initially drawn into the tank and prior to its mixing with previously heated water that is still retained within the tank as a result of water flow occasioned by use of hot water in the system. The advantageous objective is to attempt to maintain a previously heated portion of the water at the desired elevated temperature so that there is at least some heated water available for immediate use while the system is recovering from a prior water use.
There have been numerous recent attempts to design and develop hot water heating systems that can efficiently and effectively utilize heat pump systems of the type which are being used for space heating purposes. An example of such a system is illustrated in U.S. Pat. No. 4,098,092 granted on July 4, 1978 to Kanwal N. Singh who is also the inventor of the hot water heating system disclosed herein. The system disclosed in that patent is designed to provide space heating or cooling of a residence with a by-product use being that of heating water for use in the water system of the residence. The system as disclosed in that patent to effect the heating of the water merely comprises providing of an additional water storage tank with a heat exchanger coupled with a heat pump system to provide a transfer of heat to the water when the situation warranted the utilization of the heat pump.
While the system, as disclosed in the cited patent, does provide the advantageous obtaining of heat for the heating of water, the system is not as fully efficient as is desired to effectively and efficiently utilize electrical power. The location and arrangement of a heat exchanger within the water tank, wherein the refrigerant fluid is caused to circulate and thus effect the heat transfer, relies on thermally convective currents developed within the tank for effecting this operation. Since thermal convective currents that may be developed within a storage tank of water are not of a rapid flow type, such systems relying on thermal convection have a relatively slow transfer of heat and the system thus disclosed in that patent is not able to attain the high efficiency of heat transfer to most effectively utilize the benefits of a heat pump system. This factor of low efficiency that is a consequence of direct immersion of a condenser/heat exchanger immersion in the water tank is also applicable to other known heat pump water heaters since they also use the direct immersion construction technique.
Another example of a combined space heating/cooling function and water heating in a residence is disclosed in U.S. Pat. No. 3,922,876 granted Dec. 2, 1975 to T. I. Wetherington, Jr., et al. That patent shows the interconnection of an air conditioner having the primary function of effecting space cooling in the residence with the water system in an attempt to conserve energy. This system has the same disadvantage as the system of U.S. Pat. No. 4,098,092 in that it is only capable of heating water during the time of its operation to provide space cooling in the residence. U.S. Pat. No. 3,188,829 issued to H. G. Siewart on June 15, 1965 also discloses a similar space heating/cooling system which has the secondary or auxiliary function of heating water for the residence. Such systems are not adequate for or capable of providing the primary source of heat for a hot water system as they are dependent on the space heating/cooling requirements or conditions for operation and those conditions are totally unrelated to the hot water requirements. Consequently, these systems will often be operating when there is no requirement for the auxiliary heating of water or they will not be operating when there is a requirement for heating of water. Furthermore, these combination systems having the primary space heating/cooling function are inefficient in their operation as to providing of heat for the water system in that the condenser heat exchanger in the water system cannot obtain all of the heat available in the refrigerant because of the existence of another condenser heat exchanger. In practical effect, this heat transfer capability is limited to about one-third of the available heat.